Radiation-sensitive device utilizing a laser beam to measure the displacement of an object

ABSTRACT

A device for continually measuring the displacement of an object utilizing a laser beam. A photoreceiver is attached to the object in such a manner as to be subject to displacement corresponding to the displacement of the object. The photoreceiver has a measuring photoelectric cell extending in the direction in which displacement is being measured. The photoelectric cell has a sensitivity which changes continuously in the direction of measurement. A source of a laser beam is positioned on a reference point, and the beam is directed toward the photocell to generate an electrical signal in response to the position of the beam on the cell. The beam is fanned out along a path which intersects and crosses the cell, and accordingly displacement of the object causes a displacement of the cell which generates a change in the electrical output. In order to produce an electrical output signal which is free from fluctuations due to causes other than the displacement of the object, a comparison photoelectric cell is disposed parallel to the measuring photocell, and the laser beam crosses the comparison cell as well. The comparison cell produces a signal which is fed to an amplifier and which may be used as a reference to compare the magnitude of the output from the measuring photoelectric cell. In addition, the amplifier for the comparison cell may be self adjusting to produce a constant output and may be coupled to the amplifier at the output of the measuring cell to control the amplification factor thereof. In this way, the amplification can be varied without losing the reference as a means for determining the displacement of the measuring cell.

Waited States aterit Thorn et a1.

[54] RADIATION-SENSITIVE DEVICE [57] ABSCT UTILIZING A LASER BEAM To Adevice for continually measuring the displacement of an ob- MEASURE THED P AC M OF N ject utilizing a laser beam. A photoreceiver is attachedto the OBJECT object in such a manner as to be subject to displacementcorresponding to the displacement of the object. The pho- [72] lnvmtorsThom Horst toreceiver has a measuring photoelectric cell extending inthe Mumch of n! direction in which displacement is being measured. The[7 3] Assignee: Siemens Aktiengesells lmft, Be lin and photoelectriccell has a sensitivity which changes continuously Munich, Germany in thedirection of measurement. A source of a laser beam is positioned on areference point, and the beam is directed [22] 1970 toward the photocellto generate an electrical signal in [211 App]. No.: 19,330 response tothe position of the beam on the cell. The beam is fanned out along apath which intersects and crosses the cell, and accordingly displacementof the object causes a displace- [301 Forelgn Application Pnomy Dam mentof the cell which generates a change in the electrical out- Mar. 17,1969 Germany ..P 19 133 99.4 put. in order to produce an electricaloutput signal which is free from fluctuations due to causes other thanthe displace- [52] U.S. Cl ..250/23] R, 250/21 1 K, 250/209 ment of theobject, a comparison photoelectric cell is disposed [51] Int. Cl.parallel to the measuring photocell, and the laser beam crosses Field OfSearch 211 the comparison cell as well. The comparison cell produces a356/167, 172 signal which is fed to an amplifier and which may be usedas a reference to compare the magnitude of the output from the [56]Reierences Clted measuring photoelectric cell. In addition, theamplifier for the comparison cell may be self adjusting to produce aconstant UNITED STATES PATENTS output and may be coupled to theamplifier at the output of 2,879,405 3/1959 Pankove ..250/211 themeasuring cell to control the amplification factor thereof. 3,087,069 4/1963 Moncrieff-Yeates. 250/211 In this way, the amplification can bevaried without losing the 3,159,750 12/1964 Kazan 250/231 reference as ameans for determining the displacement of the 3,193,686 7/1965 Heinz...250/211 measuring cell. 3,258,601 6/1966 Su1eski. ..250/211 3,354,31111/1967 Vali a a1 ..250/234 x 99 .3 a

Primary Examiner-Walter S tolwei n V a MAM AttorneyHill, Sherman,Meroni, Gross & Simpson PHOTOELECTR| PHOTOELECTRIC CELL CEL L 1 1. 2 i VV V2 S CONTROL H CIRCUIT S12 DIFFERENTIAL AMPLIF I ER LRECORDERRADIATION-SENSITIVE DEVICE UTILIZING A LASER BEAM TO MEASURE THEDISPLACEMENT OF AN OBJECT BACKGROUND OF THE INVENTION Field of theInvention The field of art to which this invention pertains is a meansfor measuring continuous displacements of objects and particularly ofstructural objects using a laser beam. In particular, the presentinvention relates to a device for measuring substantial displacements inthe order of magnitude of several centimeters as well as for measuringconsiderably smaller displacements.

SUMMARY OF THE INVENTION It is a principal feature of the presentinvention to provide an improved device for the measurement of adisplacement of an object.

It is another feature of the present invention to provide a device forutilizing a laser beam to continually measure the shifting of an object.

It is an important object of the present invention to provide animproved laser beam measuring system.

It is also an object of the present invention to provide a laser beamdisplacement-measuring system which produces an electrical outputdirectly in response to the displacement of an object being measured.

It is also an object of the present invention to provide adisplacement-measuring device using a photoelectric cell having asensitivity which increases along the length of the cell and forimpinging a fanned out laser beam across the cell to generate an outputin response to movement of the cell with respect to the beam.

It is another object of the present invention to provide a laser beammeasuring system as described above wherein the photoelectric cell has asensitivity which increases nonlinearly and in such a manner as toproduce a linear electrical output.

It is an additional object of the present invention to provide acomparison photoelectric cell in parallel relation with a measuringphotocell wherein the comparison cell has a substantially constant widthalong the length thereof and wherein the measuring cell has acontinually changing width to vary the sensitivity thereof, and whereina fanned-out laser beam is caused to cross both the comparison andmeasuring cell to produce separate output signals therefrom.

It is another object of the present invention to provide a laser beamdisplacement-measuring system as described above wherein each of thephotoelectric cells have amplifiers coupled to the output thereof andwherein the amplifier at the output of the comparison cell is asubstantially constant output amplifier to provide a reference signalfor the measuring cell output signal.

It is a further object of the present invention to provide a measuringsystem as described above wherein the constant output amplifier iscoupled to the amplifier at the output of the measuring cell to controlthe amplification thereof and thereby provide a self-adjusting andcontinuous reference signal for the measurement of the displacements ofthe measuring photocell.

It is also an object of the present invention to provide a system asdescribed above wherein a differential amplifier and a recorder arecoupled to the outputs of each of the photoelectric cells.

It is still another object of the present invention to providephotoelectric cells which increase in opposite directions so thatmovements of the cell in either direction with respect to a laser beamwill produce an increasing electrical output.

These and other objects, features and advantages of the invention willbe readily apparent from the following description of a preferredembodiment thereof, taken in conjunction with the accompanying drawings,although variations and modifications may be efiected without departingfrom the spirit and scope of the novel concepts of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustrating thepositioning of a comparison photoelectric cell and a measuringphotoelectric cell side by side and showing the orientation of afanned-out laser beam which crosses both of the photocells to generateseparate output signals.

FIG. 2 is an illustration of another embodiment of the present inventionin which a pair of oppositely arranged measuring photocells are used inconjunction with a constant width comparison cell.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention relates toa device for measuring the displacement or shifting of an object using alaser beam mounted on a reference plane. A photoreceiving device isattached to the object to be measured and has a variable sensitivity sothat relative motion between the photoreceiving device and the laserbeam will generate changing electrical signals.

Devices for the continuous measurement of shifting or displacement ofstructures are required for numerous uses. For instance, in theconstruction industry, it is often required to measure continuously thedeformation of walls, bridge piers or the like. In taking suchmeasurements, it is often impossible to find a reference level for themeasurement since the ground and surrounding areas often deform with thestructure being measured. This is principally true in the case of makingload tests for bridge piers where measurements of deformation have to bemade continuously over a period of several hours while the pier is undera certain load.

Such measurements are primarily done optically. In this case, anobserver watches the position of a mark on the object being measuredfrom a place sufficiently far away to be free of deformations. This isoften done with the help of a telescope. However, such a system is oftenexpensive due to the high cost of the expertise required in making thesemeasurements.

Prior devices have utilized laser beams for the purpose of controllingthe position of a machine or the like. These devices, however, are notsuitable for long period recording of the shifting or displacement of anobject. One of the problems has been to find a means for dealing withfluctuations in the operation of laser beams which could distortreadings over a period of time. Also, prior devices have been capable ofmeasuring only small displacements rather than displacements in theorder of several centimeters which are possible by the presentinvention.

The present invention provides an apparatus which is capable of makingsuch measurements. In the present system, a laser beam originates from areference position and is directed onto a measuring photoelectric cellwhich is disposed to move with the shifting or deformation of the objectbeing measured. The photoelectric cell has an absolute sensitivity whichchanges continuously in the direction in which the measuring is beingaccomplished. This sensitivity is brought about by a variation in thewidth of the cell from one end to the other.

It may be desirable to vary the width of the cell in a nonlinear mannerso that the output from the cell will increase linearly withdisplacement. The nonlinearity of the photocell arrangement is requireddue to the unequal distribution of the radiation density of the fannedout laser beam.

In the alternate, a constant width photoelectric cell may be used and afilter may be arranged between the cell and the source of the laser beamin such a way that the filter changes its permeability continuously inthe measurement direction. The filter, for instance, may be anabsorption filter with the constant value of absorption increasingcontinuously from one end of the filter to the other.

Such a filter arrangement has the advantage of producing increasingsensitivity of the cell without requiring increasing width. In this way,a much narrower photocell can be utilized.

In order to determine the absolute position of the laser beam on thephotoelectric cell and thereby to obtain a measurement of the absolutedisplacement of the object being measured, the present inventionprovides that a comparison photoelectric cell may be arranged parallelto the measuring cell. The comparison cell may have a constantsensitivity along its length. The fanned-out laser beam is then causedto impinge simultaneously on both the comparison cell and the measuringcell. Both of the photoelectric cells may be arranged on the load sideof a differential amplifier.

The outputs of both of the photoelectric cells may be coupled torespective amplifiers. The comparison photocell may be coupled to anamplifier which is self adjusting and which provides a constant outputsignal. The output of this amplifier may then be used to control theamplification of the amplifier coupled to the output of the measuringphotoelectric cell. In this way, a constant reference may be providedfor the amplified measuring signal even though the level ofamplification may be changed to suit the requirements of the system.

In a system using the pair of amplifiers with the comparison amplifiercontrolling the amplification of the measuring amplifier, a differentialstage may be omitted in view of the cost of output of the comparisonamplifier.

A recorder may be used to provide a continuous record of the amount ofdeformation or shifting of the object being measured over a period oftime. The recorder would simply be coupled to the output of theamplifiers from the respective photoelectric cells.

A system according to the present invention can also be used to detecttwistings or bendings of an object by utilizing a second measuringphotoelectric cell having an absolute sensitivity which changes in thesame direction as the sensitivity of the first measuring cell. Adifferential amplifier may be coupled to the output. A bending motionwould produce a variation of the longitudinal shifting between the twomeasuring photoelectric cells such that their output signals wouldchange unequally.

A system according to the present invention may also be utilizedadvantageously to control machines or apparatus. It is possible todetermine the nominal position of a machine and utilize increases anddecreases of the output signal from the measuring cell to operate acontrol and return the machine to its nominal plane.

Preferably to accomplish such a control according to this invention, twomeasuring photoelectric cells are to be provided having an absolutesensitivity which changes continuously in opposite directions such thatthe cells effectively increase in width from a center point between thecells. An amplifier is preferably arranged on the load side of each cellwhich can be adjusted by a constant output amplifier as alreadydescribed. In this case also a comparison photoelectric cell may beprovided, and this would extend the entire length of both of themeasuring photoelectric cells so that only one automatically adjustingamplifier need be provided.

The above arrangement can be expanded so that machines are guided alonga straight line or the like.

In further expanding the concepts embodied in the present invention, alaser beam can be utilized which produces two beams and wherein thereceiver consists of two combined arrangements of measuringphotoelectric cells which extend along one side of a right angle. Otherarrangements, of course, may be proposed.

Referring to the drawings in greater detail, FIG. I shows twophotoelectric cells 1 and 2 having their longitudinal direction linedgenerally parallel to the measuring direction which is indicated by thedouble arrow 2a.

The measuring photoelectric cell 2 has a photosensitive plane whichwidens continuously in the longitudinal direction. The width of thecomparison photoelectric cell is constant over the entire length. Bothcells are fixed to the object being measured.

A laser beam 3 is provided from a suitable source which source isdisposed on a reference plane. The beam 3 is fanned out as shown andcrosses both the cells 1 and 2.

If the object being measured shifts in position, the cells 1 and 2 willbe displaced and signals S and S, will be generated from the cells. Itis apparent that the signal S: will remain constant with the variationsin relative position of the laser beam 3, while variations in the signalS will increase or decrease with the changing relative positions betweenthe beam 3 and the widened cell 2.

To accomplish an absolute calibration of the system, namely acalibration which is independent of laser efiiciency in variousenvironmental conditions which accompany the shifting of the objectbeing measured over a period of time, an automatically adjustedamplifier V. is arranged on the load side of the comparisonphotoelectric cell. This amplifier has an amplification which changesautomatically to produce a constant output signal S The amplifier V isthen coupled to a control system a and from the system 4 to an amplifierV The amplifier V, is coupled to the output of the measuringphotoelectric cell 2 and has its amplification adjusted by the signalcoming from the amplifier V The outputs of both of the amplifiers V andV, are coupled to a differential amplifier 5.

The differential amplifier 5 could be omitted in the arrangement shownin FIG. 1 due to the presence of the constant adjusting amplifier V andthe coupling of the output of that amplifier to the further amplifier VThe laser radiation may also be modulated to increase the sensitivity ofoperation. Also, modulation has the advantage of reducing the effects ofdaylight or other straight light from the environment. Such straightlight can be suppressed in a modulated system by the use of selectivelyabsorbing filters or the like.

In FIG. 2, a similar type arrangement is provided which may be used forthe control of the movement of a machine along a plane. Thephotoreceiver which is attached to the machine contains twophotoelectric cells 12 and 13 which are arranged to have increasingsensitivities in opposite directions from a common center point 13a.

A comparison photoelectric cell is provided parallel to the twophotoelectric cells 12 and 13 and has an output connected to anautomatically adjusting amplifier V The amplifier V corresponds to theamplifier V in FIG. 1 and is coupled to further amplifiers V and V overcircuits 14.

A shifting or displacement of the laser beam 3 with respect to the loadcells generates an output signal in either direction which can then beutilized to control the machine operations with respect to a given planeor line of movement. Here also, the relative motion between the beam andthe cells is caused by the shifting of the photoelectric cells which arecoupled in a suitable manner to the machine. The laser source is rigidlypositioned on a reference plane at a distant point.

Such a device as described above has the advantage that the continuousadjustment of the machine is possible and not simply an adjustment aftera given deviation is exceeded. By providing a similar receiver as shownin FIG. 2 both laterally and vertically and providing so-called crossfanned laser beams, an arrangement is provided for the control orguidance of a machine along a straight line.

The present invention is not limited to the specific arrangementsdescribed above. Especially, it is not necessary that these controls beused to guide a machine along a plane or along a straight line but couldalso be used for different proportional controls corresponding to theshifting of the machine other than simply returning the machine to anominal position.

The use of a comparison photoelectric cell assures that the distancedifferences between the laser and the receiving arrangement do not haveany effect on the system output. This is especially true in the case ofmoving machines being controlled whereby an overloading of theamplifiers could be accomplished when the machine is closest to thesource of the laser energy.

We claim as our invention:

1. A system for continually measuring the amount of displacement of anobject relative to a reference plane comprismg:

means mounting a first measuring photoelectric cell on said object insuch a manner as to be subject to a displacement in accordance with thedisplacement of said object,

said first measuring photoelectric cell having an absolute sensitivitywhich changes continuously in the direction of the displacement to bemeasured,

a reference point,

a source of a laser beam originating from said reference point,

said laser beam being fanned out in a direction intersecting andcrossing said photoelectric cell,

a comparison photoelectric cell being arranged on said objectsubstantially parallel to said measuring photoelectric cell, saidcomparison photoelectric cell having a substantially constant absolutesensitivity along its length,

electrical means coupled to the outputs of said photocells and using thecombined outputs to develop a resultant signal, whereby displacement ofsaid object and hence of said first measuring photoelectric cell causessaid laser beam to sweep said first measuring photoelectric cell andgenerate an electrical signal which is indicative of the amount ofdisplacement of said object.

2. A displacement measuring system in accordance with claim 1 whereinsaid photoelectric cell contains a photosensitive plane having a widthwhich increases from one end of the cell to the other along thedirection of displacement being measured.

3. A displacement measuring system in accordance with claim 2 whereinthe increase in the width of the cell along the length thereof isnonlinear such that the output signal generated from the cell changeslinearly with the sweeping of the beam along the length of the cell.

4. A displacement measuring system in accordance with claim 1 whereinsaid photoelectric cell includes a filter having a filter characteristicwhich changes continuously in the direction of the displacement to bemeasured.

5. A displacement measuring system in accordance with claim 4 whereinsaid filter is an absorption type filter having a permeability whichincreases essentially wedgelike along the direction of measurement.

6. A displacement system in accordance with claim 1 wherein a first selfadjusting amplifier is coupled to the output of the comparisonphotoelectric cell, said self adjusting amplifier producing asubstantially constant output, a further amplifier coupled to the outputof the measuring photoelectric cell, and means coupling an output ofsaid first amplifier to said further amplifier to control theamplification thereof.

7. A displacement system in accordance with claim 6 wherein a recorderis coupled to the outputs of said first and further amplifiers.

8. A displacement system in accordance with claim 1 wherein adifferential amplifier is coupled to the outputs of said photoelectriccells.

9. A displacement system in accordance with claim 1 wherein a secondmeasuring photoelectric cell is provided oppositely of said firstmeasuring photoelectric cell and has increasing sensitivity in adirection oppositely of the direction of increasing sensitivity of saidfirst measuring photoelectric cell, whereby the displacement of a movingobject along a plane can be determined relative to a fixed line oftravel.

1. A system for continually measuring the amount of displacement of anobject relative to a reference plane comprising: means mounting a firstmeasuring photoelectric cell on said object in such a manner as to besubject to a displacement in accordance with the displacement of saidobject, said first measuring photoelectric cell having an absolutesensitivity which changes continuously in the direction of thedisplacement to be measured, a reference point, a source of a laser beamoriginating from said reference point, said laser beam being fanned outin a direction intersecting and crossing said photoelectric cell, acomparison photoelectric cell being arranged on said objectsubstantially parallel to said measuring photoelectric cell, saidcomparison photoelectric cell having a substantially constant absolutesensitivity along its length, electrical means coupled to the outputs ofsaid photocells and using the combined outputs to develop a resultantsignal, whereby displacement of said object and hence of said firstmeasuring photoelectric cell causes said laser beam to sweep said firstmeasuring photoelectric cell and generate an electrical signal which isindicative of the amount of displacement of said object.
 2. Adisplacement measuring system in accordance with claim 1 wherein saidphotoelectric cell contains a photosensitive plane having a width whichincreases from one end of the cell to the other along the direction ofdisplacement being measured.
 3. A displacement measuring system inaCcordance with claim 2 wherein the increase in the width of the cellalong the length thereof is nonlinear such that the output signalgenerated from the cell changes linearly with the sweeping of the beamalong the length of the cell.
 4. A displacement measuring system inaccordance with claim 1 wherein said photoelectric cell includes afilter having a filter characteristic which changes continuously in thedirection of the displacement to be measured.
 5. A displacementmeasuring system in accordance with claim 4 wherein said filter is anabsorption type filter having a permeability which increases essentiallywedgelike along the direction of measurement.
 6. A displacement systemin accordance with claim 1 wherein a first self adjusting amplifier iscoupled to the output of the comparison photoelectric cell, said selfadjusting amplifier producing a substantially constant output, a furtheramplifier coupled to the output of the measuring photoelectric cell, andmeans coupling an output of said first amplifier to said furtheramplifier to control the amplification thereof.
 7. A displacement systemin accordance with claim 6 wherein a recorder is coupled to the outputsof said first and further amplifiers.
 8. A displacement system inaccordance with claim 1 wherein a differential amplifier is coupled tothe outputs of said photoelectric cells.
 9. A displacement system inaccordance with claim 1 wherein a second measuring photoelectric cell isprovided oppositely of said first measuring photoelectric cell and hasincreasing sensitivity in a direction oppositely of the direction ofincreasing sensitivity of said first measuring photoelectric cell,whereby the displacement of a moving object along a plane can bedetermined relative to a fixed line of travel.